Riding Mower Only Turns On When Choke Is Engaged 

After starting your lawnmower engine, turning the throttle off will immediately shut it off. The engine will keep on chugging along despite the choke being fully closed.

Using the choke will increase the fuel consumption of the engine. If you don’t take care of this, the mower’s performance could suffer and the engine could break down.

If too much air or not enough gasoline is being allowed into the engine, a Cub Cadet lawn mower may only start when the choke is engaged.

Possible causes include a filthy carburetor, low fuel quality, a clogged fuel filter, a malfunctioning fuel pump, a leaking gas cap, a broken fuel line, or a leaking carburetor gasket.

When in doubt about how to use your riding mower safely, consult the instructions that came with it. It’s important to take precautions like this before attempting to make any repairs, such as removing the ignition key and spark plug boot.

Reasons why your riding mower won’t start unless you use the choke

  • A failure to provide fuel
  • Used fuel
  • Lack of cleanliness in the carburetor
  • Fuel line clog
  • Faulty gas pump
  • Fuel filter is clogged
  • Flawed gas cap
  • Way too much oxygen
  • Faulty gasket in the carburetor
  • Fuel line puncture

riding mower

7 Causes Why Riding Mower Only Runs With the Choke Engaged

Using Antiquated Fuel in a Mower

Old gas is frequently at the root of the problem when an engine is not getting enough fuel. After 30 days, gas might start to go bad and become unsafe to use.

Most gasoline contains ethanol, which can damage a small engine like the one used in a riding mower. Water will condense in the fuel system if ethanol is used.

Varnish and deposits left behind by this mixture will eventually lead to the breakdown of fuel system components and fuel limitation if left unchecked. There is a lot of corrosiveness in this combo as well.

This is why you should only use recently purchased gas and use it up within 30 days.

Riding mowers can only run on unleaded gasoline with an octane level of 87 or above and no more than 10% ethanol. Never fill up with gas that has more than 10% ethanol in it.

Here you may learn how to choose the best gas for your riding mower.

The ANSWER is to get rid of the stale gas in the tank. Using a fuel additive like Sea Foam Motor Treatment or STA-BIL in addition to new gas can assist clean the fuel system and minimize moisture.

As a bonus, it will prevent the gas from decomposing as quickly, extending its useful life. Learn the reasons why I use Sea Foam in all of my portable motors.

Inspecting a Riding Mower’s Filthy Carburetor

To control the ratio of fuel to air in an internal combustion engine, a carburetor is installed. Fuel passages and internal parts might become clogged and nonfunctional when it becomes unclean, most frequently owing to old gas.

The engine will not operate smoothly until the carburetor is either cleaned or replaced.

A riding mower’s carburetor can be removed and cleaned by the owner, if they are mechanically inclined and not afraid of fiddly jobs involving small parts.

Even if you follow all of these methods to clean the carburetor, there’s still a chance that it won’t start up properly. If you don’t feel like cleaning or rebuilding the carburetor yourself, have a small engine mechanic handle it.

Damage to or Blockage of a Riding Mower’s Fuel Line

It is possible for the engine to overheat if the fuel line is punctured and air is sucked into the line. Alternatively, the engine may not get enough gasoline if the pipe becomes clogged.

In either case, the mower may refuse to start unless the choke is engaged, since the choke is used to regulate the amount of air entering the engine and hence the fuel-to-air ratio for combustion.

The ANSWER is to check the gasoline lines. Locate the carburetor by following the fuel line upstream. Check for holes or rips that could let air into the gas tank.

The next thing you should do is look for a blockage in the fuel line, which would prevent enough gas from getting to the engine. The fuel shut-off valve must be used first to stop the flow of fuel. To collect fuel, cut off a length of the fuel line and set the cut end in a suitable container.

After resuming fuel flow, make sure fuel is flowing freely from the fuel line and into the storage tank. Turn off the gas and disconnect the fuel line from the mower if the fuel flow is poor.

Carburetor cleaning can be sprayed into the line to help break up the obstruction. The next step, using compressed air to clear the obstruction, is a good idea. As often as required.

If the gasoline line is too clogged or damaged to be cleaned, or if you locate a puncture, you should replace the affected portion with a new one of the same diameter.

Riding Mower’s Clogged Fuel Filter

Between the fuel lines, you’ll find the fuel filter, whose job it is to prevent debris like dirt and debris from entering the fuel system and wearing out the engine.

A yearly replacement is required to ensure the functioning of this component. If the gasoline filter becomes clogged, the flow of fuel to the engine may be diminished.

When the amount of fuel in the tank is low, the choke is utilized to adjust the gas-to-air mixture for proper combustion.

A new inline gasoline filter can be installed in place of the old one once the clogged filter is removed.

The filter housing should have a directional arrow on one side. To ensure proper fuel flow, the filter should be inserted with the arrow pointing in the direction of the fuel flow.

A Riding Mower’s Defective Fuel Pump

If the carburetor on your riding mower is located in a location that is higher than the gasoline tank, you will need to utilize a fuel pump. To transfer gas from the tank to the carburetor, the majority of riding mowers employ a vacuum pump that draws suction from the motor.

Verify that fuel is entering the pump’s inlet port when performing a fuel pump test. Next, you’ll want to disconnect the fuel line from the carburetor and test the fuel flow into a container.

A new fuel pump should be installed if insufficient fuel flow is being delivered or if any cracks or fuel leaks are discovered.

Riding Mower with a Leaking Carburetor Gasket

The gasket that forms a seal behind the carburetor of a riding mower may eventually wear out or disintegrate. If the engine is running too lean, it could be due to a faulty gasket that is allowing extra air to be sucked into the system.

When an engine is “running lean,” it is receiving more air than it needs and a smaller amount of gasoline than normal. To counteract the additional air being sucked into the engine due to the faulty gasket, the choke must be applied.

Check the carburetor to see if its bolts are tight and the gasket is undamaged.

If the gasket has stopped sealing, you can get to the carburetor by dismantling the supporting linkages and nuts. Take off the gasket and carburetor.

After replacing the gasket, the carburetor, bolt, and links can be reattached. While the carburetor is out of the mower, you can inspect it to see if it needs to be cleaned.

Inadequate Gas Cap on a Riding Mower

There needs to be a way for air to get into the gasoline tank through a vent. When the vent is blocked, no air can enter the fuel tank, creating a vacuum. This vacuum is preventing fuel from reaching the carburetor.

The gas cap on a riding mower serves as a vent for the gasoline tank. To determine if a vacuum has formed, you can use a pressure gauge or the following procedures:

  • To let air into the gas tank, loosen the cap.
  • You should turn the choke off.
  • If the engine keeps running with the choke turned off, the cap could be faulty.
  • You should attempt a replication of the situation to verify the bad cap.
  • Make sure the top is securely fastened and keep the engine running without the throttle.
  • It’s probably a bad cap if the engine starts to sputter after a time and won’t run smoothly unless you unscrew the cap.

Substitute the gas cap if it’s faulty.

Does Your Ride-On Mower Still Give You Trouble?

When you’ve had a lawn mower for a while, it’s bound to develop some kind of issue. There are a wide variety of issues that might arise with a riding mower, such as when it smokes, cuts unevenly, loses power, won’t start, leaks fuel, and so on.

View this helpful resource featuring charts detailing typical issues and their solutions with riding mowers:
Solutions to the Most Frequent Issues with Riding Lawnmowers.

To get help with your riding mower if you are unable to or unable to do so yourself, contact a local lawn mower dealership or repair shop.